The Off Broadway Affair - S3-E10
Plot hole: U.N.C.L.E.'s pen communicators worked much like modern cell phones: when one agent called another, they "rang" with a 2-tone signal. For some reason in this episode, Solo's pen, which isn't on an open circuit, transmits Illya's voice without ringing first. It signals normally a few scenes later, though. (00:27:55 - 00:34:15)
Answer: He must have ridden in an Eaton's store elevator while he was in Canada at some point. For some reason, this elevator reminds him of it. The show's original concept had Solo being a Canadian, so this may be a minor nod to that fact.
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